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Introduction: The catecholaminergic component of the brain-pituitary-gonadal axis, which mediates the influence of external and internal stimuli on the central nervous system and gonad development in vertebrates, is largely unexplored in Chondrichthyes. We considered Scyliorhinus canicula (L., 1758) females as a model for this vertebrate's class, to assess the involvement of the catecholaminergic system of the brain in its reproduction. Along the S. canicula reproductive cycle, we characterized and evaluated differences in somata morphometry and the number of putative catecholaminergic neurons in two brain nuclei: the periventricular preoptic nucleus, hypothesized to be a positive control for ovarian development, and the suprachiasmatic nucleus, examined as a negative control. Materials andmethods: 16 S. canicula wild females were sampled and grouped in maturity stages (immature, maturing, mature, and mature egg-laying). The ovary was histologically processed for the qualitative description ofmaturity stages. Anti-tyrosine hydroxylase immunofluorescence was performed on the diencephalic brain sections. The immunoreactive somata were investigated for morphometry and counted using the optical fractionator method, throughout the confocal microscopy. Results and discussions: Qualitative and quantitative research confirmed two separate populations of immunoreactive neurons. The modifications detected in the preoptic nucleus revealed that somata were more numerous, significantly smaller in size, and more excitable during the maturing phase but decreased, becoming slightly bigger and less excitable in the egg-laying stage. This may indicate that the catecholaminergic preoptic nucleus is involved in the control of reproduction, regulating both the onset of puberty and the imminent spawning. In contrast, somata in the suprachiasmatic nucleus grew in size and underwent turnover in morphometry, increasing the total number from the immature-virgin to maturing stage, with similar values in the more advanced maturity stages. These changes were not linked to a reproductive role. These findings provide new valuable information on Chondrichthyes, suggesting the existence of an additional brain system implicated in the integration of internal and environmental cues for reproduction. [ABSTRACT FROM AUTHOR]

While the general diet of Mediterranean elasmobranchs has been widely studied, little is known about food partitioning and competition among sympatric species, despite these being important forces structuring marine communities. Using stomach content and stable isotope analyses, we investigated diet and trophic levels and evaluated the diet overlap and partitioning of Scyliorhinus canicula, Mustelus mustelus, and M. punctulatus in the northwestern Adriatic Sea. These shark species were confirmed as opportunistic mesopredators, but significant differences in their diets emerged. The two bentho-demersal Mustelus species had a larger trophic overlap with S. canicula than between each other. Given the pronounced morphological similarity of these two Mustelus species, this is likely a strategy to limit competition. The strictly benthic S. canicula showed a more varied diet compared to the other species. Stable isotope analysis highlighted that despite the smaller size and overlapping diets, S. canicula occupied a slightly higher trophic level. A better characterization of the trophic role of these species in the food web of the basin can be obtained from these data. At an ecosystem level, this information is essential to evaluate the possible consequences of the decline or recovery of the population of these exploited species. [ABSTRACT FROM AUTHOR]

IntroductionThe catecholaminergic component of the brain-pituitary-gonadal axis, which mediates the influence of external and internal stimuli on the central nervous system and gonad development in vertebrates, is largely unexplored in Chondrichthyes. We considered Scyliorhinus canicula (L., 1758) females as a model for this vertebrate's class, to assess the involvement of the catecholaminergic system of the brain in its reproduction. Along the S. canicula reproductive cycle, we characterized and evaluated differences in somata morphometry and the number of putative catecholaminergic neurons in two brain nuclei: the periventricular preoptic nucleus, hypothesized to be a positive control for ovarian development, and the suprachiasmatic nucleus, examined as a negative control.Materials and methods16 S. canicula wild females were sampled and grouped in maturity stages (immature, maturing, mature, and mature egg-laying). The ovary was histologically processed for the qualitative description of maturity stages. Anti-tyrosine hydroxylase immunofluorescence was performed on the diencephalic brain sections. The immunoreactive somata were investigated for morphometry and counted using the optical fractionator method, throughout the confocal microscopy.Results and discussionsQualitative and quantitative research confirmed two separate populations of immunoreactive neurons. The modifications detected in the preoptic nucleus revealed that somata were more numerous, significantly smaller in size, and more excitable during the maturing phase but decreased, becoming slightly bigger and less excitable in the egg-laying stage. This may indicate that the catecholaminergic preoptic nucleus is involved in the control of reproduction, regulating both the onset of puberty and the imminent spawning. In contrast, somata in the suprachiasmatic nucleus grew in size and underwent turnover in morphometry, increasing the total number from the immature-virgin to maturing stage, with similar values in the more advanced maturity stages. These changes were not linked to a reproductive role. These findings provide new valuable information on Chondrichthyes, suggesting the existence of an additional brain system implicated in the integration of internal and environmental cues for reproduction.

Electroreception is an intriguing sense in the animal kingdom, that confers an advantage, when other senses cannot be used. Many shark and ray species spend a prolonged embryonic life stage enclosed in an egg case, where the avoidance of predators is difficult. In this study, we found that late stages of small-spotted catshark (Scyliorhinus canicula) exhibit a freeze response that stops ventilation when exposed to electric stimuli. The embryos also showed a short-term tolerance buildup, when exposed to several electrical stimuli over a 40-min period. Surprisingly, the embryos also reacted with a freeze response when the electrical field was turned off, indicating that the embryos reacted to a change in electrical field, rather than the presence of one. Younger embryos showed a significantly longer freeze response than older embryos. This study documents the use of electroreception in small-spotted catshark embryos as a possible predator avoidance response. [ABSTRACT FROM AUTHOR]

The retinoic acid (RA) pathway was shown to be important for tooth development in mammals, and suspected to play a key role in tooth evolution in teleosts. The general modalities of development of tooth and "tooth-like" structures (collectively named odontodes) seem to be conserved among all jawed vertebrates, both with regard to histogenesis and genetic regulation. We investigated the putative function of RA signalling in tooth and scale initiation in a cartilaginous fish, the small-spotted catshark Scyliorhinus canicula. To address this issue, we identified the expression pattern of genes from the RA pathway during both tooth and scale development and performed functional experiments by exposing small-spotted catshark embryos to exogenous RA or an inhibitor of RA synthesis. Our results showed that inhibiting RA synthesis affects tooth but not caudal primary scale development while exposure to exogenous RA inhibited both. We also showed that the reduced number of teeth observed with RA exposure is probably due to a specific inhibition of tooth bud initiation while the observed effects of the RA synthesis inhibitor is related to a general delay in embryonic development that interacts with tooth development. This study provides data complementary to previous studies of bony vertebrates and support an involvement of the RA signalling pathway toolkit in odontode initiation in all jawed vertebrates. However, the modalities of RA signalling may vary depending on the target location along the body, and depending on the species lineage. [ABSTRACT FROM AUTHOR]

The retinoic acid (RA) pathway was shown to be important for tooth development in mammals, and suspected to play a key role in tooth evolution in teleosts. The general modalities of development of tooth and “tooth-like” structures (collectively named odontodes) seem to be conserved among all jawed vertebrates, both with regard to histogenesis and genetic regulation. We investigated the putative function of RA signalling in tooth and scale initiation in a cartilaginous fish, the small-spotted catshark Scyliorhinus canicula. To address this issue, we identified the expression pattern of genes from the RA pathway during both tooth and scale development and performed functional experiments by exposing small-spotted catshark embryos to exogenous RA or an inhibitor of RA synthesis. Our results showed that inhibiting RA synthesis affects tooth but not caudal primary scale development while exposure to exogenous RA inhibited both. We also showed that the reduced number of teeth observed with RA exposure is probably due to a specific inhibition of tooth bud initiation while the observed effects of the RA synthesis inhibitor is related to a general delay in embryonic development that interacts with tooth development. This study provides data complementary to previous studies of bony vertebrates and support an involvement of the RA signalling pathway toolkit in odontode initiation in all jawed vertebrates. However, the modalities of RA signalling may vary depending on the target location along the body, and depending on the species lineage.

Shark populations have suffered dramatic declines across the world as a result of overfishing.Marine protected areas (MPAs) can help restore overfished populations; however, their effectiveness largely relies on understanding the ecology of the targeted species.This study investigated the spatial ecology of the intensely harvested but understudied small spotted catshark (Scyliorhinus canicula) through acoustic telemetry in the Cíes Islands, a small MPA in the north‐west of the Iberian Peninsula.There were significant effects of diel, seasonal cycles, biotic (sex and total length) and abiotic (bottom sea temperature) variables on the spatial behaviour of S. canicula. The mean residency index was low (0.27) and movement patterns suggested a strong connection with inshore waters. While the probability of presence in the study area was mainly driven by sex (i.e. greater for females), a drastic increase in activity was observed at night (compared with daytime hours). The activity space decreased with larger body sizes. Warmer waters were related to higher activity levels and larger activity spaces.This study provides essential knowledge of the spatial behaviour of S. canicula, with significant implications for the conservation and management of this species. The results indicate that small MPAs may fail to protect the whole range of movements of S. canicula, but suggest a larger protection potential for females.To be effective for S. canicula conservation, MPAs should be appropriately sized and designed for the ranging behaviour of the target species in order to provide total protection. Temporal restrictions on fishing at night mirroring the peak activity pattern of S. canicula could be implemented to limit the probability of its capture. [ABSTRACT FROM AUTHOR]

The hypothalamus is a key vertebrate brain region involved in survival and physiological functions. Understanding hypothalamic organization and evolution is important to deciphering many aspects of vertebrate biology. Recent comparative studies based on gene expression patterns have proposed the existence of hypothalamic histogenetic domains (paraventricular, TPa/PPa; subparaventricular, TSPa/PSPa; tuberal, Tu/RTu; perimamillary, PM/PRM; and mamillary, MM/RM), revealing conserved evolutionary trends. To shed light on the functional relevance of these histogenetic domains, this work aims to interpret the location of developed cell groups according to the prosomeric model in the hypothalamus of the catshark Scyliorhinus canicula, a representative of Chondrichthyans (the sister group of Osteichthyes, at the base of the gnathostome lineage). To this end, we review in detail the expression patterns of ScOtp, ScDlx2, and ScPitx2, as well as Pax6-immunoreactivity in embryos at stage 32, when the morphology of the adult catshark hypothalamus is already organized. We also propose homologies with mammals when possible. This study provides a comprehensive tool to better understand previous and novel data on hypothalamic development and evolution. [ABSTRACT FROM AUTHOR]

Shark populations that are distributed alongside a latitudinal gradient often display body size differences at sexual maturity and vicariance patterns related to their number of tooth files. Previous works have demonstrated that Scyliorhinus canicula populations differ between the northeastern Atlantic Ocean and the Mediterranean Sea based on biological features and genetic analysis. In this study, we sample more than 3,000 teeth from 56 S. canicula specimens caught incidentally off Roscoff and Banyuls-sur-Mer. We investigate population differences based on tooth shape and form by using two approaches. Classification results show that the classical geometric morphometric framework is outperformed by an original Random Forests-based framework. Visually, both S. canicula populations share similar ontogenetic trends and timing of gynandric heterodonty emergence but the Atlantic population has bigger, blunter teeth, and less numerous accessory cusps than the Mediterranean population. According to the models, the populations are best differentiated based on their lateral tooth edges, which bear accessory cusps, and the tooth centroid sizes significantly improve classification performances. The differences observed are discussed in light of dietary and behavioural habits of the populations considered. The method proposed in this study could be further adapted to complement DNA analyses to identify shark species or populations based on tooth morphologies. This process would be of particular interest for fisheries management and identification of shark fossils. [ABSTRACT FROM AUTHOR]

The hypothalamus is a key vertebrate brain region involved in survival and physiological functions. Understanding hypothalamic organization and evolution is important to deciphering many aspects of vertebrate biology. Recent comparative studies based on gene expression patterns have proposed the existence of hypothalamic histogenetic domains (paraventricular, TPa/PPa; subparaventricular, TSPa/PSPa; tuberal, Tu/RTu; perimamillary, PM/PRM; and mamillary, MM/RM), revealing conserved evolutionary trends. To shed light on the functional relevance of these histogenetic domains, this work aims to interpret the location of developed cell groups according to the prosomeric model in the hypothalamus of the catshark Scyliorhinus canicula, a representative of Chondrichthyans (the sister group of Osteichthyes, at the base of the gnathostome lineage). To this end, we review in detail the expression patterns of ScOtp, ScDlx2, and ScPitx2, as well as Pax6-immunoreactivity in embryos at stage 32, when the morphology of the adult catshark hypothalamus is already organized. We also propose homologies with mammals when possible. This study provides a comprehensive tool to better understand previous and novel data on hypothalamic development and evolution.

Shark populations that are distributed alongside a latitudinal gradient often display body size differences at sexual maturity and vicariance patterns related to their number of tooth files. Previous works have demonstrated that Scyliorhinus canicula populations differ between the northeastern Atlantic Ocean and the Mediterranean Sea based on biological features and genetic analysis. In this study, we sample more than 3,000 teeth from 56 S. canicula specimens caught incidentally off Roscoff and Banyuls-sur-Mer. We investigate population differences based on tooth shape and form by using two approaches. Classification results show that the classical geometric morphometric framework is outperformed by an original Random Forests-based framework. Visually, both S. canicula populations share similar ontogenetic trends and timing of gynandric heterodonty emergence but the Atlantic population has bigger, blunter teeth, and less numerous accessory cusps than the Mediterranean population. According to the models, the populations are best differentiated based on their lateral tooth edges, which bear accessory cusps, and the tooth centroid sizes significantly improve classification performances. The differences observed are discussed in light of dietary and behavioural habits of the populations considered. The method proposed in this study could be further adapted to complement DNA analyses to identify shark species or populations based on tooth morphologies. This process would be of particular interest for fisheries management and identification of shark fossils.

Simple Summary: In catsharks (Scyliorhinus canicula), air exposure induces amino acid catabolism altogether with osmoregulatory imbalances. This study describes a novel NHE isoform being expressed in gills that may be involved in ammonium excretion. Acute-stress situations in vertebrates induce a series of physiological responses to cope with the event. While common secondary stress responses include increased catabolism and osmoregulatory imbalances, specific processes depend on the taxa. In this sense, these processes are still largely unknown in ancient vertebrates such as marine elasmobranchs. Thus, we challenged the lesser spotted catshark (Scyliorhinus canicula) to 18 min of air exposure, and monitored their recovery after 0, 5, and 24 h. This study describes amino acid turnover in the liver, white muscle, gills, and rectal gland, and plasma parameters related to energy metabolism and osmoregulatory imbalances. Catsharks rely on white muscle amino acid catabolism to face the energy demand imposed by the stressor, producing NH4+. While some plasma ions (K+, Cl− and Ca2+) increased in concentration after 18 min of air exposure, returning to basal values after 5 h of recovery, Na+ increased after just 5 h of recovery, coinciding with a decrease in plasma NH4+. These changes were accompanied by increased activity of a branchial amiloride-sensitive ATPase. Therefore, we hypothesize that this enzyme may be a Na+/H+ exchanger (NHE) related to NH4+ excretion. The action of an omeprazole-sensitive ATPase, putatively associated to a H+/K+-ATPase (HKA), is also affected by these allostatic processes. Some complementary experiments were carried out to delve a little deeper into the possible branchial enzymes sensitive to amiloride, including in vivo and ex vivo approaches, and partial sequencing of a nhe1 in the gills. This study describes the possible presence of an HKA enzyme in the rectal gland, as well as a NHE in the gills, highlighting the importance of understanding the relationship between acute stress and osmoregulation in elasmobranchs. [ABSTRACT FROM AUTHOR]

In bony vertebrates, skeletal mineralization relies on the secretory calcium-binding phosphoproteins (Scpp) family whose members are acidic extracellular proteins posttranslationally regulated by the Fam20°C kinase. As scpp genes are absent from the elephant shark genome, they are currently thought to be specific to bony fishes (osteichthyans). Here, we report a scpp gene present in elasmobranchs (sharks and rays) that evolved from local tandem duplication of sparc-L 5′ exons and show that both genes experienced recent gene conversion in sharks. The elasmobranch scpp is remarkably similar to the osteichthyan scpp members as they share syntenic and gene structure features, code for a conserved signal peptide, tyrosine-rich and aspartate/glutamate-rich regions, and harbor putative Fam20°C phosphorylation sites. In addition, the catshark scpp is coexpressed with sparc-L and fam20°C in tooth and scale ameloblasts, similarly to some osteichthyan scpp genes. Despite these strong similarities, molecular clock and phylogenetic data demonstrate that the elasmobranch scpp gene originated independently from the osteichthyan scpp gene family. Our study reveals convergent events at the sparc-L locus in the two sister clades of jawed vertebrates, leading to parallel diversification of the skeletal biomineralization toolkit. The molecular evolution of sparc-L and its coexpression with fam20°C in catshark ameloblasts provides a unifying genetic basis that suggests that all convergent scpp duplicates inherited similar features from their sparc-L precursor. This conclusion supports a single origin for the hypermineralized outer odontode layer as produced by an ancestral developmental process performed by Sparc-L, implying the homology of the enamel and enameloid tissues in all vertebrates. [ABSTRACT FROM AUTHOR]

Development of tooth shape is regulated by the enamel knot signalling centre, at least in mammals. Fgf signalling regulates differential proliferation between the enamel knot and adjacent dental epithelia during tooth development, leading to formation of the dental cusp. The presence of an enamel knot in non-mammalian vertebrates is debated given differences in signalling. Here, we show the conservation and restriction of fgf3, fgf10, and shh to the sites of future dental cusps in the shark (Scyliorhinus canicula), whilst also highlighting striking differences between the shark and mouse. We reveal shifts in tooth size, shape, and cusp number following small molecule perturbations of canonical Wnt signalling. Resulting tooth phenotypes mirror observed effects in mammals, where canonical Wnt has been implicated as an upstream regulator of enamel knot signalling. In silico modelling of shark dental morphogenesis demonstrates how subtle changes in activatory and inhibitory signals can alter tooth shape, resembling developmental phenotypes and cusp shapes observed following experimental Wnt perturbation. Our results support the functional conservation of an enamel knot-like signalling centre throughout vertebrates and suggest that varied tooth types from sharks to mammals follow a similar developmental bauplan. Lineage-specific differences in signalling are not sufficient in refuting homology of this signalling centre, which is likely older than teeth themselves.

While cartilage is an ancient tissue found both in protostomes and deuterostomes, its mineralization evolved more recently, within the vertebrate lineage. SPARC , SPARC-L , and the SCPP members (Secretory Calcium-binding PhosphoProtein genes which evolved from SPARC-L) are major players of dentine and bone mineralization, but their involvement in the emergence of the vertebrate mineralized cartilage remains unclear. We performed in situ hybridization on mineralizing cartilaginous skeletal elements of the frog Xenopus tropicalis (Xt) and the shark Scyliorhinus canicula (Sc) to examine the expression of SPARC (present in both species), SPARC-L (present in Sc only) and the SCPP members (present in Xt only). We show that while mineralizing cartilage expresses SPARC (but not SPARC-L) in Sc , it expresses the SCPP genes (but not SPARC) in Xt , and propose two possible evolutionary scenarios to explain these opposite expression patterns. In spite of these genetic divergences, our data draw the attention on an overlooked and evolutionarily conserved peripheral cartilage subdomain expressing SPARC or the SCPP genes and exhibiting a high propensity to mineralize. [ABSTRACT FROM AUTHOR]

Aim: Trypanorhyncha cestodes comprise a wide range of heteroxenous parasites infecting elasmobranchs as definitive hosts. Limited data exist on the larval infection of these cestodes and the role of intermediate and paratenic hosts in the life cycle of these parasites. We investigated the factors that determine the occurrence and the level of infection of Grillotia plerocerci in the skeletal muscles of various benthonic sharks and analyzed the parasites through an integrative taxonomic approach. Location: Mediterranean Sea. Methods: Sharks obtained as bycatch of commercial trawling activities (i.e., Etmopterus spinax, Galeus melastomus, and Scyliorhinus canicula) were used in this study. Data from a limited number of Dalatias licha and Scyliorhinus stellaris were also included. Grillotia plerocerci were molecularly characterized using the partial 28S large subunit rDNA. Boosted regression trees were used to model the relationship between the abundance of infection with both morphological and physiological predictors in each host. Results: Plerocerci of Grillotia were detected in all shark species except S. stellaris. Host species significantly differed in terms of parasite abundance, with the highest and lowest prevalence and abundance of infection detected in G. melastomus and E. spinax, respectively. The relative influence of the traits involved in explaining the parasite abundance was related to the host size in G. melastomus, while both morphology‐ and physiology‐related traits explained the patterns observed in E. spinax and S. canicula. The 28S rDNA sequences shared an identity of ∼99.40% with a Grillotia species previously found in the Mediterranean Sea. At intraspecific level, two different genotypes were found. A first type was retrieved only from D. licha, whereas a second type was found in G. melastomus, E. spinax, and S. canicula. Main conclusions: Present results suggest that the two genotypes could be involved in different consumer‐resource systems and confirm most of the examined shark species as transport hosts of Grillotia species for unknown larger top predators. [ABSTRACT FROM AUTHOR]

While cartilage is an ancient tissue found both in protostomes and deuterostomes, its mineralization evolved more recently, within the vertebrate lineage. SPARC, SPARC-L, and the SCPP members (Secretory Calcium-binding PhosphoProtein genes which evolved from SPARC-L) are major players of dentine and bone mineralization, but their involvement in the emergence of the vertebrate mineralized cartilage remains unclear. We performed in situ hybridization on mineralizing cartilaginous skeletal elements of the frog Xenopus tropicalis (Xt) and the shark Scyliorhinus canicula (Sc) to examine the expression of SPARC (present in both species), SPARC-L (present in Sc only) and the SCPP members (present in Xt only). We show that while mineralizing cartilage expresses SPARC (but not SPARC-L) in Sc, it expresses the SCPP genes (but not SPARC) in Xt, and propose two possible evolutionary scenarios to explain these opposite expression patterns. In spite of these genetic divergences, our data draw the attention on an overlooked and evolutionarily conserved peripheral cartilage subdomain expressing SPARC or the SCPP genes and exhibiting a high propensity to mineralize.

The anatomy of sharks, rays, and chimaeras (chondrichthyans) is crucial to understanding the evolution of the cranial system in vertebrates due to their position as the sister group to bony fishes (osteichthyans). Strikingly different arrangements of the head in the two constituent chondrichthyan groups—holocephalans and elasmobranchs—have played a pivotal role in the formation of evolutionary hypotheses targeting major cranial structures such as the jaws and pharynx. However, despite the advent of digital dissections as a means of easily visualizing and sharing the results of anatomical studies in three dimensions, information on the musculoskeletal systems of the chondrichthyan head remains largely limited to traditional accounts, many of which are at least a century old. Here, we use synchrotron tomographic data to carry out a digital dissection of a holocephalan and an elasmobranch widely used as model species: the elephantfish, Callorhinchus milii, and the small‐spotted catshark, Scyliorhinus canicula. We describe and figure the skeletal anatomy of the head, labial, mandibular, hyoid, and branchial cartilages in both taxa as well as the muscles of the head and pharynx. In Callorhinchus, we make several new observations regarding the branchial musculature, revealing several previously unreported or ambiguously characterized muscles, likely homologous to their counterparts in the elasmobranch pharynx. We also identify a previously unreported structure linking the pharyngohyal of Callorhinchus to the neurocranium. Finally, we review what is known about the evolution of chondrichthyan cranial muscles from their fossil record and discuss the implications for muscle homology and evolution, broadly concluding that the holocephalan pharynx is likely derived from a more elasmobranch‐like form which is plesiomorphic for the chondrichthyan crown group. This dataset has great potential as a resource, particularly for researchers using these model species for zoological research, functional morphologists requiring models of musculature and skeletons, as well as for palaeontologists seeking comparative models for extinct taxa. [ABSTRACT FROM AUTHOR]

Most extant vertebrates display a high variety of tooth and tooth‐like organs (odontodes) that vary in shape, position over the body and nature of composing tissues. The development of these structures is known to involve similar genetic cascades and teeth and odontodes are believed to share a common evolutionary history. Gene expression patterns have previously been compared between mammalian and teleost tooth development but we highlight how the comparative framework was not always properly defined to deal with different tooth types or tooth developmental stages. Larger‐scale comparative analyses also included cartilaginous fishes: sharks display oral teeth and dermal scales for which the gene expression during development started to be investigated in the small‐spotted catshark Scyliorhinus canicula during the past decade. We report several descriptive approaches to analyse the embryonic tooth and caudal scale gene expressions in S. canicula. We compare these expressions wih the ones reported in mouse molars and teleost oral and pharyngeal teeth and highlight contributions and biases that arise from these interspecific comparisons. We finally discuss the evolutionary processes that can explain the observed intra and interspecific similarities and divergences in the genetic cascades involved in tooth and odontode development in jawed vertebrates. [ABSTRACT FROM AUTHOR]

Eighty-five specimens of the lesser spotted dogfish, Scyliorhinus canicula Linnaeus, 1758, was caught by a bottom trawl in the international waters of the Mersin Bay in May 2018. Some of the caught individuals were preserved in 4% formalin and was deposited in the Museum of the Systematic, Faculty of Fisheries, Mersin University, (catalogue number: MEUFC-18-11-079). The depth of sampling area is between 274 and 641 m. A total of 13 trawling operations were carried out. The total number of caught individuals was 85 and on average 5 individuals were caught in each operation. The other cartilaginous fishes caught apart from S. canicula were Galeus melastomus (1 individual), Squalus acanthias (4 individuals), Etmopterus spinax (11 individuals) and S. canicula made up 84.16% of all cartilaginous fishes which were caught.

In this study, we investigated ontogenetic and sexual changes of the brain scaling as well as the scaling and the relative size of six major brain areas in the small-spotted catshark Scyliorhinus canicula from the Mediterranean Sea. The brain somatic index (0.31–1.25%) did not differ significantly between sexes but was significantly affected by size with smaller specimens exhibiting higher values. Brain growth exhibited negative allometry (allometric coefficient 0.634), not affected by sex or maturity status. The brain growth rate was found to be higher compared with a previous study from the Atlantic Ocean. Regarding the scaling of the brain areas, the olfactory bulbs scaled with positive allometry, the telencephalon and the diencephalon scaled with the same rate of negative allometry, the mesencephalon exhibited even higher negative allometry, while the cerebellum and the medulla oblongata both followed a close-to-isometric growth pattern. Immature S. canicula possessed a larger mesencephalon and diencephalon, highlighting the importance of vision in this life period, while mature specimens had enlarged olfactory bulbs, indicating that olfaction may be more important after the animal attains sexual maturity. In respect of sexual dimorphism, males had a larger cerebellum and medulla oblongata, while females had enlarged telencephalon and olfactory bulbs. [ABSTRACT FROM AUTHOR]

Corticosteroids are hormones produced in vertebrates exerting gluco- and mineralocorticoid actions (GC and MC) mediated by specific receptors (GR and MR, respectively). In elasmobranchs, the major circulating corticosteroid is the 1α-hydroxycorticosterone (1α-OHB). This hormone acts as a MC, but to date its role as a GC has not been established. As there is no 1α-OHB standard available, here we employed a set of in vivo and ex vivo approaches to test GC actions of other corticosteroids in the lesser spotted catshark (Scyliorhinus canicula). Dexamethasone (DEX, a synthetic corticosteroid) slow-release implants decreased plasma 1α-OHB levels after 7 days, and modified carbohydrates metabolism in liver and white muscle (energy stores and metabolic enzymes). In addition, ex vivo culture of liver and white muscle explants confirmed GC actions of corticosteroids not naturally present in sharks (cortisol and DEX) by increasing glucose secretion from these tissues. Dose–response curves induced by cortisol and DEX, altogether with the use of specific GR inhibitor mifepristone, confirmed the involvement of GR mediating glucose secretion. This study highlights the influence of corticosteroids in the glucose balance of S. canicula, though the role of 1α-OHB as a GC hormone in sharks should be further confirmed.

Atmospheric CO2 levels have been rising due to an increase in anthropic activities and its implications over marine ecosystems are unprecedented. The present study focused on the effects of ocean acidification (OA) on key hematological parameters of the juvenile small‐spotted catsharks (Scyliorhinus canicula). Eggs were reared throughout the entire embryogenesis (~4 months) plus 5 additional months, in two experimental treatments (control: pCO2 ~ 400 μatm; and high CO2: pCO2 ~ 900 μatm, Δ −0.3 pH units). After blood collection, the following hematological parameters were evaluated: (a) normal blood cells count (erythrocytes, leukocytes, and thrombocytes), (b) presence of erythrocytes with nuclear abnormalities, and (c) erythrocyte nucleus to cytoplasmic ratio. Concomitantly, to determine the cardiac and hematopoietic conditions, the spleen and heart to body ratios were also assessed. The present findings indicate that the measured variables may not be affected by elevated pCO2 in this temperate species, as no significant differences were observed between treatments across all the endpoints tested. Nonetheless, it is worth mentioning a decreasing trend observed in a number of thrombocytes associated with OA, which should foster further investigation, regarding other aspects of their coagulation response. Along with OA, other stressors are expected to impact marine life, such as warming and hypoxia. Thus, future research should aim to investigate the cumulative effect of these stressors on hematological parameters in sharks. HIGHLIGHTS: Hematological parameters were evaluated in temperate sharks exposed to high CO2 (OA). Measured variables may not be affected by elevated pCO2, since no significant differences were observed between treatments. Although there was a decreasing trend observed in the number of thrombocytes associated with OA. [ABSTRACT FROM AUTHOR]

Background: Glycosaminoglycans (GAGs), including hyaluronic acid (HA), dermatan sulfate (DS) and chondroitin sulfate (CS) are essential components of the bone and cartilage tissues. CS isolated from the cartilage tissue of various animals has found application in pharmaceuticals, cosmetics and food industries. In the first part of the present work, three methods were used and compared to extract and purify glycosaminoglycans (GAGs) from the cartilage powder of a local cartilaginous marine species «Scyliorhinus canicula». One of these GAGs, chondroitin sulfate (CS), will be exploited for the development of an anti-osteoarthritis generic at the request of a collaborative pharmaceutical industry. Thus this active ingredient must meet the requirements and tests described by the European Pharmacopoeia (Ph. Eur.). These tests are treated in the second part of this work. Results: Among the three methods that have been applied in the present work, in order to optimize the best process for GAGs preparation, enzymatic hydrolysis with papain followed by deproteinisation using trichloroacetic acid (TCA) was found the best one. The separation of the extracted GAGs using agarose gel electrophoresis, and the identification of bands by Fourier Transform Infrared (FT-IR) Spectroscopy, revealed that the cartilage GAGs of « Scyliorhinus canicula» are exclusively chondroitin sulfate (CS) and dermatane sulfate (DS), with proportions of 12.889 and 87.111% respectively, and that CS is of type C. The extraction technique with papain provides a product with GAGs content of around 90%. The TCA deproteinisation yielded the lowest level of protein (2.8%) in the extracted GAGs, less than 3%, which is the standard required by the European Pharmacopoeia (Ph. Eur.). Cetylpyridinium chloride (CPC) assay suggests that the titration technique, although is introduced by the Ph. Eur. for the determination of CS content, is not an accurate method, and that the values obtained by the optimized and validated HPLC method, described in this work, are more exact. Conclusion: The extracted and purified active ingredient is perfectly conform to the tests described by the Ph. Eur. The results suggest that the co-product of Scyliorhinus canicula would be a perfect source of molecules of pharmacological interest, obtained by a simple and non-agressive process. [ABSTRACT FROM AUTHOR]

Glucocorticoids are pleiotropic steroid hormones mediating redistribution of energy. They induce breakdown of glycogen stores and consequent plasma hyperglycaemia after stressful situations. Glucocorticoid actions in most vertebrate species are exerted by cortisol and corticosterone. However, 1α-hydroxycorticosterone is the dominant corticosteroid hormone in elasmobranchs, though its effects as a glucocorticoid are unknown. Here we demonstrate, by using ultra-performance liquid chromatography coupled to tandem mass spectrometry for the quantification of 1α-hydroxycorticosterone in plasma of the elasmobranch Scyliorhinus canicula, the response of this hormone to an acute-stress situation and for the first time its glucocorticoid action in elasmobranchs. After an acute air-exposure challenge, S. canicula increased plasma levels of 1α-hydroxycorticosterone altogether with enhanced glycolysis and gluconeogenesis pathways to fuel energy demanding tissues, such as white muscle, during the first hours after the stress situation. We foresee our study as a starting point to evaluate stress responses in elasmobranchs, as well as for future applications in the management of these key ecosystem species.

In 2019, Europe will adopt a no-discards policy in fisheries. This entails the landing of captured species unless strong evidence is provided supporting their survival and recovery after fishing. Thus, research on this topic is gaining momentum. Bottom-trawling, as a non-selective fishing method, is characterized by a high proportion of discards including vulnerable key species, such as demersal sharks. Their survival may also depend on capture depth. By paralleling onboard and laboratory experiments with the small-spotted catshark, Scyliorhinus canicula , we offer a robust experimental design to assess the survival of discarded sharks. Catsharks were captured by bottom-trawling at two depths (shallow ~89 m and deep ~479 m). Blood samples were collected following trawl capture and analyzed for stress biomarkers (lactate, osmolality, phosphate, urea). During recovery in onboard tanks, behavior was video-recorded and fish were re-sampled after 24 h. A second experiment was conducted in laboratory facilities to simulate air-exposure after trawling and to analyze the physiological recovery. Our results showed that 95.7% of the animals survived 24 h after trawling. We confirmed that trawling elicited acute stress responses in catshark but that they managed to recover. This was demonstrated by lactate concentrations that were 2.6 mM upon capture, but recovered to assumed baselines after 24 h (0.2 mM). Non-invasive video monitoring revealed behavioral differences with depth, whereby those captured at 89 m depth required longer to recover than those captured at 479 m depth. Implementation of standardized survival studies by fishery managers can benefit from holistic physiological approaches, such as the one proposed here. • Physiological recovery and survival rates of a bottom-trawled shark were evaluated. • A new methodology for discard survival evaluation in bottom-trawling fisheries is described. • The lesser-spotted catshark (Scyliorhinus canicula) shows high survival and recovery rates. • This holistic approach may pave the way for the evaluation of commercial fish species. [ABSTRACT FROM AUTHOR]

Abstract The present study describes histochemical and immunohistochemical characteristics of the spiral valve and its associated lymphoid tissue (GALT) in the dogfish Scyliorhinus canicula. The mucosal surface of the spiral valve represents the first line of defense against pathogens coming from the external environment through food. Epithelial, mucus and immune cells play a key role in controlling the inflammatory response. Valve intestine of S. canicula had many folds lined by simple columnar cells and goblet cells, which later reacted positive to PAS, AB and AB-PAS, histochemical stains differentiated the different types of mucins; lectin histochemistry (PNA and WGA), detected neutral and acid mucins secreted that plays an important role in protection against invading pathogens. Integrin α5β1 was expressed in enterocytes that line the valve's folds with greater marking in the apical part of the cells. Laminin was found on the apical side of the epithelium, in fibrillar and cellular elements of the lamina propria and in the muscularis mucosa. In the spiral valve gut-associated lymphoid tissue (GALT) has been studied. For the first time, massive leucocytes aggregates were identified by confocal immunofluorescence techniques, using the following antibodies: TLR2, S100, Langerin/CD207. Our results expand knowledge about Dogfish valve intestine giving important news in understanding comparative immunology. Highlights • Gut-associated lymphoid tissue (GALT) constitutes leucocytes reserve. • Immunity antibodies highlight intraepithelial lymphocytes protection role. • Spiral valve mucosae acts against food-derived pathogens in shark. [ABSTRACT FROM AUTHOR]

Throughout the animal kingdom chemical senses are one of the primary means by which organisms make sense of their environment. To achieve perception of complex chemosensory stimuli large repertoires of olfactory and gustatory receptors are employed in bony vertebrates, which are characterized by high evolutionary dynamics in receptor repertoire size and composition. However, little is known about their evolution in earlier diverging vertebrates such as cartilaginous fish, which include sharks, skates, rays, and chimeras. Recently, the olfactory repertoire of a chimera, elephant shark, was found to be curiously reduced in odorant receptor number. Elephant sharks rely heavily on electroreception to localize prey; thus, it is unclear how representative their chemosensory receptor repertoire sizes would be for cartilaginous fishes in general. Here, we have mined the genome of a true shark, Scyliorhinus canicula (catshark) for olfactory and gustatory receptors, and have performed a thorough phylogenetic study to shed light on the evolution of chemosensory receptors in cartilaginous fish. We report the presence of several gustatory receptors of the TAS1R family in catshark and elephant shark, whereas TAS2R receptors are absent. The catshark olfactory repertoire is dominated by V2R receptors, with 5–8 receptors in the other three families (OR, ORA, TAAR). Species-specific expansions are mostly limited to the V2R family. Overall, the catshark chemosensory receptor repertoires are generally similar in size to those of elephant shark, if somewhat larger, showing similar evolutionary tendencies across over 400 Myr of separate evolution between catshark and elephant shark. [ABSTRACT FROM AUTHOR]

Abstract Cartilaginous dogfish Scyliorhinus canicula continued to transfer four anthropogenic radionuclides (65Zn, 60Co, 134Cs and 241Am) to their eggs for over six months, after two months of continued maternal exposure to radio-labelled food. Unexpectedly, rates of radionuclide transfers to eggs and their yolk & embryo during maternal depuration were equivalent for 60Co and 241Am, or even enhanced for 65Zn and 134Cs by factors of c.200–350%, over two-three months, compared to their maximal transfer rates at the end of the maternal uptake phase. These rates of maternal transfer of radionuclides to yolk & embryo were positively associated with their previously determined efficiencies of assimilation (AE) from ingested radio-labelled food. Thus progeny may be more exposed via maternal transfer to those radionuclides which have greater rates of maternal assimilation from food. As maternal depuration continued beyond 60–80 up to 180–200 days the transfers of all four radionuclides to eggs did diminish but were still substantial at mean values of 18% for 241Am, 17% for 134Cs and 9 and 8% for 60Co and 65Zn, respectively. In the yolk & embryo the mean rates of transfer over this period were further reduced for 241Am (13.5%), 60Co (2.5%) and 65Zn (5.8%), but were still appreciable for 134Cs at 56%. These results for S. canicula have demonstrated a potential enhanced radiological risk of extended duration due to the particular biokinetics of maternal transfer in this species. This study draws further attention to the current paucity of knowledge about the maternal: progeny transfer pathway, particularly in the context of the known heightened radio-sensitivity of early life stages in fish and other vertebrates, compared to later life stages. Highlights • Depurating dogfish transfer radionuclides to eggs over six months. • Transfers even enhanced for 65Zn and 134Cs. • Progeny more exposed to radionuclides with greater assimilation from food. [ABSTRACT FROM AUTHOR]

The parasitic fauna of the small-spotted catshark, Scyliorhinus canicula in the north-eastern Aegean Sea was investigated. Twenty-one out of the 52 (prevalence 40.4%) specimens collected were found infected with parasites; an arthropod and two nematode genera. Seven specimens (prevalence 13.5%) were infected by a Neoalbionella sp. copepod. Ten and 14 specimens were infected by the nematodes Proleptus obtusus (prevalence 19.2%) and Anisakis sp. (prevalence 26.9%), respectively. Female S. canicula specimens were significantly more heavily infected during autumn and when the whole sampling period is considered. Nematode infection was significantly related to season, becoming progressively heavier from spring to autumn. No correlation was found between TL of specimens and number of parasites for males or females, irrespective of gender. The present study provided a first record of Neoalbionella sp., P. obtusus and Anisakis sp. infections of S. canicula in the north-eastern Mediterranean. The lower prevalence of Proleptus obtusus and the higher prevalence of Anisakis sp. infection recorded in this study may be due to prey availability and parasite populations in this locality. [ABSTRACT FROM AUTHOR]

Embryological stages of oviparous elasmobranch during development can be difficult to identify, requiring magnification and/or fixation of an anaesthetized embryo. These restrictions are poorly suited for monitoring the development of living elasmobranchs inside their egg cases. There are two major aims of this study. The first was to observe elasmobranch embryonic development non-invasively and produce a non-invasive developmental key for identifying the life stages for an elasmobranch inside the egg case. To this end, 7 key developmental stages were identified for the greater spotted catshark, Scyliorhinus stellaris, and are provided here with diagrams from multiple perspectives to demonstrate the key features of each stage. The physiological and ecological relevance of each stage are discussed in terms of structure and function for embryonic survival in the harsh intertidal zone. Also discussed is the importance of the egg case membrane and the protective embryonic jelly. The second aim of the study was to understand the applicability of the 7 developmental stages from S. stellaris to other oviparous elasmobranchs. Thus, changes in embryonic body size and egg yolk volume at each stage were measured and compared with those of the closely related, lesser spotted catshark, Scyliorhinus canicula. We find nearly identical growth patterns and yolk consumption patterns in both species across the 7 developmental stages. Thus, although the 7 developmental stages have been constructed in reference to the greater spotted catshark, we suggest that it can be applied to other oviparous elasmobranch species with only minor modification. [ABSTRACT FROM AUTHOR]

This study examines the diet of lesser spotted dogfish Scyliorhinus canicula, one of the most ubiquitous predators of European coastal waters. This species is of increasing ecological significance as other large predatory fish decline as it has known interactions with fisheries. Scyliorhinus canicula diet was investigated in Irish coastal waters during June and July 2014 using both stomach‐content analysis and δ13C and δ15N stable‐isotope ratios. Prey contribution to the diet from dual stable‐isotope data was estimated using Bayesian mixing models. It was found that only stable‐isotope analysis provided a time‐integrated picture of the diet of S. canicula and allowed for a new estimation of their trophic position. Trophic positions from stomach‐content analysis within the present study and previous studies were found to be higher than revealed by isotopes. Stomach‐content analysis could not reveal the importance of soft‐bodied animals in the diet of these fish, however this approach remains a valuable tool to understand the potential prey spectrum in advance of isotope analysis and allows for a better resolution down to species level. The results highlight a greater variety in the diet of this important predator and the benefit of taking a multidisciplinary approach in dietary studies. [ABSTRACT FROM AUTHOR]

Abstract Concentrations of 6 trace metals (Ag, Cd, Cu, Ni, Pb, Zn) in the muscle of 2 sharks (Galeus melastomus and Scyliorhinus canicula), 4 teleosts (Helicolenus dactylopterus , Lepidorhombus boscii , Micromesistius poutassou and Phycis blennoides) and 1 crustacean (Nephrops norvegicus) were compared between the Bay of Biscay (Atlantic Ocean) and the Gulf of Lions (Mediterranean Sea). Although average concentrations and the trace element pollution index were generally higher in the Gulf of Lions, significant differences between the two ecosystems were only found for Zn for Helicolenus dactylopterus , and for Ag and Cu for the crustacean N. norvegicus. Moreover, some relationships between trophic level or size and metal concentrations were found for these two species. The absence of clear pattern may result from the blurring effect of contamination and excretion that may act differentially for all species and all elements. Highlights • Low concentrations of trace metals in the muscle tissue for all studied marine species • Absence of clear patterns for all studied species and elements • Metal concentrations were mainly higher in the Gulf of Lions than in the Bay of Biscay. [ABSTRACT FROM AUTHOR]

Studying the feeding ecology of an organism is essential to understanding its ecological role in the ecosystem. Although the small-spotted catshark ( Scyliorhinus canicula ) is widely studied, most feeding studies have been conducted using invasive techniques, such as the analysis of stomach contents. Moreover, information from the Mediterranean Sea is surprisingly scarce and not up to date. Here, we studied the feeding ecology of the small-spotted catshark in the northwestern Mediterranean Sea using stable isotopes (nitrogen and carbon isotopic values) from blood samples, with individuals released alive in the area of capture after sampling. In overall for the population of small-spotted catshark, the isotopic values were −19.01 ± 1.12‰ and 8.03 ± 0.61‰ for δ 13 C and for δ 15 N, respectively. Results reveal a diet mainly composed of euphausiids, with sex and size variations. Results confirm the ecological role of the small-spotted catshark as a mesopredator, which holds a trophic position similar to skates and rays in the study area, but lower than the other demersal and pelagic sharks analysed. The trophic behaviour of the small-spotted catshark indicates its high trophic plasticity, which could allow this species to thrive in highly exploited environments. Our methodological approach, which did not damage the target species, presents new possibilities for conducting ecological studies with other elasmobranchs in the Mediterranean Sea, a highly exploited area that hosts many threatened and rare species. [ABSTRACT FROM AUTHOR]

Photo‐identification (photo‐ID) was tested as a means to identify individual small‐spotted catsharks Scyliorhinus canicula. The spotting pattern of the caudal region of S. canicula was used for the tests and revealed that photo‐ID is an efficient method to identify individuals. Photo‐ID is logistically simple, making it a potential alternative to traditional tagging to provide information on the distribution patterns and population dynamics of S. canicula and related species. [ABSTRACT FROM AUTHOR]

The hypothalamus is a key integrative center of the vertebrate brain. To better understand its ancestral morphological organization and evolution, we previously analyzed the segmental organization of alar subdivisions in the catshark Scyliorhinus canicula, a cartilaginous fish and thus a basal representative of gnathostomes (jawed vertebrates). With the same aim, we deepen here in the segmental organization of the catshark basal hypothalamus by revisiting previous data on ScOtp, ScDlx2/5, ScNkx2.1, ScShh expression and Shh immunoreactivity jointly with new data on ScLhx5, ScEmx2, ScLmx1b, ScPitx2, ScPitx3a, ScFoxa1, ScFoxa2 and ScNeurog2 expression and proliferating cell nuclear antigen (PCNA) immunoreactivity. Our study reveals a complex genoarchitecture for chondrichthyan basal hypothalamus on which a total of 21 microdomains were identified. Six belong to the basal acroterminal region, the rostral-most point of the basal neural tube; seven are described in the tuberal region (Tu/RTu); four in the perimamillar region (PM/PRM) and four in the mamillar one (MM/RM). Interestingly, the same set of genes does not necessarily describe the same microdomains in mice, which in part contributes to explain how forebrain diversity is achieved. This study stresses the importance of analyzing data from basal vertebrates to better understand forebrain diversity and hypothalamic evolution. [ABSTRACT FROM AUTHOR]

This study concerns the cephalopod species that are part of the diet of the small-spotted catshark Scyliorhinus canicula and the longnose spurdog Squalus blainville sampled by commercial trawlers in the Aegean Sea from 2005 to 2012. Based on the examined cephalopod beaks, 15 species were identified belonging in six families of Teuthida, one of Sepiida and two of Octopoda. The diversity of cephalopod prey species was higher for S. canicula (N = 15) than for S. blainville (N = 10). Nektonic cephalopods comprised the majority (>72%) of the preyed species by both sharks, among which about 55% inhabit the demersal zone and 45% the mesopelagic. In the diet of S. canicula, the demersal squid Illex coindetii and the pelagic sepiolid Heteroteuthis dispar were equally represented composing 20% of prey specimens, followed by the small-sized squid Abralia veranyi and the demersal sepiolid Rossia macrosoma. The latter species was substituted in the diet of S. blainville by the demersal medium-sized octopod Scaeurgus unicirrhus, which with the equally represented three other species, composed 50% of the cephalopod prey. Differences observed between S. canicula and S. blainville in the condition of beaks retained in their stomach contents and in the variation of prey species diversity by predator specimen size, may imply differences in their foraging tactics (hunting for prey vs scavenging on the bottom), habitats and stomach evacuation frequency. [ABSTRACT FROM PUBLISHER]

The spotted catshark ( Scyliorhinus canicula) and the blackmouth catshark ( Galeus melastomus) are demersal sharks showing a distinct bathymetric distribution in the western Mediterranean. Together, both species represent more than 85% of the total abundance of demersal chondrichthyans in this Mediterranean basin. Our study provides a complete analysis of the genetic population structure, connectivity and demographic history of both species. Sampling was performed across four geographical subareas (GSAs) established by the General Fisheries Commission for the Mediterranean in the western Mediterranean: the northern Alboran Sea (GSA01), Alboran Island (GSA02), Balearic Islands (GSA05) and northern Spain (GSA06). Three mitochondrial fragments were analyzed for both species, and 12 microsatellite loci for S. canicula. We found contrasting patterns of population structure and connectivity in both species. Scyliorhinus canicula displayed significant genetic differences and low connectivity between some GSAs corresponding to different sub-basins (Alboran vs. Balearic). In contrast, G. melastomus showed absence of a population structure and high connectivity between GSAs. These findings are in accordance with the fact that both species exhibit different dispersal behaviors, which leads to distinct bathymetric distributions. Contrasting demographic histories were also identified: Scyliorhinus canicula revealed a recent stable population, with evidence of bottlenecks in the past, which may be related to Pleistocene glacial periods; whereas G. melastomus showed a recent population expansion. Altogether, our findings indicate a mismatch between fishery subareas and population structure for both sharks, which must be considered for fisheries management purposes. [ABSTRACT FROM AUTHOR]